The present disclosure relates to linear motion bearing assemblies which include components that are integrally attached to provide performance enhancing characteristics. More particularly, the present disclosure relates to linear motion bearing assemblies which include components designed to minimize the routine maintenance and enhance the performance characteristics of linear motion bearing assemblies.
Linear motion bearing assemblies or rolling element bearing assemblies of the type discussed herein are well known in the art and are typically utilized for the movement of machine parts, tools and masses. These assemblies typically include a bearing carriage mounted for movement along a shaft or along a modified Y-beam, I-beam or T-beam cross section rail. As used herein the terms rail and shaft are used interchangeably. Load bearing and return tracks are provided in association with the bearing carriage for re-circulating a plurality of rolling elements such as, for example, balls or rollers. These rolling elements travel alternately through the load bearing tracks and return tracks to facilitate movement of the bearing carriage along the rail with minimum friction.
The use of roller element bearings is especially conspicuous in the machine tool industry where requirements of accuracy, stiffness, reliability and repeatability are stringent. This type of bearing, e.g., U.S. Pat. No. 4,932,067, is typically constructed from monolithic components of both rail and carriage, with rolling elements (usually balls or rollers) disposed between the two bodies. See also U.S. Pat. No. 5,558,442. Provisions are commonly made for the circulation of the rolling elements via retainers, end caps, turnarounds or the like. Typically, provisions are also made for seals or devices intended to retain lubricant and prohibit the ingress of debris.
End caps are usually located on the ends of the bearing carriage and may have turnarounds formed therein for transferring the rolling elements from the load bearing tracks to the return tracks. The turnarounds typically comprise a semi-toroidal shaped track dimensioned and configured for the particular rolling element being employed. At the center of the semi-toroid, an internal guide may be provided to smooth the movement of the rolling elements in the turnarounds.
As can be appreciated, the operation and efficiency of a linear motion bearing is heavily influenced by the type of lubricant, the frequency the lubricant is introduced into the bearing and the amount of lubricant introduced. As a result, the performance of the bearing can be detrimentally influenced by the ingress of contaminants, such as machining chips, weld spatter, etc.
Linear motion bearing lubrication has typically been provided by 1) manual application by use of a grease gun or the like (See, for example, U.S. Pat. No. 4,932,067); 2) automatic lubrication via a centralized lubricant dispenser; or 3) through the use of rubber or synthetic resin impregnated with a lubricant and typically mounted on a carriage in position to contact a rail. (See, for example, U.S. Pat. Nos. 5,492,413, 5,494,354, 5,590,965 and 5,769,543.) Manual lubrication is very effective when the operator has access to the lubrication points. When access is limited, it is not unusual for that bearing to suffer a lubrication failure. Centralized lubrication is highly effective, but requires great expense and complication in the realization of the pump system,. the delivery lines and the attendant fittings. The lubricant impregnated rubber or synthetic resin blocks of the prior art typically require integral stiffeners or integral tensioners to facilitate uniform application of lubricant over time. The blocks are exposed to environmental conditions and contaminants.
Attempts have been made to address to these concerns and to provide self-lubricating properties to the bearing. U.S. Pat. No. 5,570,958 teaches a drawer slide type of bearing that contains a strip of lubricant-filled polymer. This strip of lubricating material contacts the rolling elements by incidental contact during re-circulation. Thus the rolling elements are intended to have sufficient lubricant on the surface as they enter the loaded region.
In the case of the ""958 patent, the incidental contact of rolling elements with the lubricating strip is not sufficient, over extended periods, to deposit consistent amounts of lubricant. Thus, under any but the least stringent applications, a lubrication failure would be expected.
Thus, it would be highly desirable to provide a linear motion bearing that is simple to assemble and acts in a consistent, self-lubricating fashion reducing environmental contamination and extending bearing life. Additionally, it would be highly desirable to provide a bearing that will remove debris attached to the rail, prohibit the ingress of contaminants and/or provide a simple means of attaching an end cap or the like for the same purpose. Lastly, it would be highly desirable to provide a bearing where these and other features may be added and/or deleted in a simple manner depending upon the particular bearing application involved.
Accordingly, the present disclosure is related to linear bearings which provide an enclosed self-lubrication system, scraping ability, enhanced sealing and other features arranged in a simple building-block manner. Further, each of the above-mentioned features may be added or omitted from the building-block arrangement depending upon the particular bearing application involved.
One embodiment of the present disclosure includes a self-lubricating bearing for supporting a load on a guide rail which includes a carriage having first and second ends, a guide surface adapted for translation atop the guide rail and an end assembly which mounts to one of the ends of the carriage. The end assembly includes a seal and a self contained lubricating assembly using a polymer block made from a synthetic lubricant composition. The lubricating assembly also includes a radially compressive housing enclosing the perimeter of the polymer block and biasing the polymer block against the guide rail to cause the synthetic lubricant to lubricate the bearing.
In one embodiment, the biasing force is accomplished by providing a mechanical interface, e.g., a T-shaped detent or a V-shaped wedge, which engages a complimentary mechanical interface, e.g., groove, formed within the polymer block. In another embodiment, the compressive housing is selectively adjustable.
Yet in another embodiment, the lubricating assembly is engaged with the end assembly in a press-fit manner and includes a plurality of radial slits to facilitate press-fit engagement within the end assembly. Still other embodiments of the present disclosure include end assemblies which include scrapers for removing excess debris from the rail during translation and positioning disks, spacers and/or alignment racks for positioning the various components of the end assembly.
One embodiment includes a self-lubricating bearing having a carriage with a guide surface adapted for translation along the guide rail and an enclosed ring-shaped end housing which mounts to at least one of the ends of the carriage. The ring-shaped end housing includes a plurality of flexible fingers arranged in spaced array about an inner periphery of the end assembly. Each of the flexible fingers biases the polymer block against a portion of the rail to consistently lubricate the rail.